Modelling and experimental studies of dielectric barrier discharges in dry and humidified air at sub-atmospheric pressure

The processes leading to the generation of reactive oxygen and nitrogen species (RONS) and hydrogen-containing species (HCS) in dielectric barrier discharges in dry and humidified air were studied both experimentally and by numerical modelling. The plasma was driven by a sinusoidal voltage with a frequency of 24 kHz at a gas pressure of 100 mbar in the case of dry air. For humidified air a 30 kHz signal was used at a gas pressure of 200 mbar. For the determination of RONS in dry air and additionally HCS in humidified air with relative humidity (RH) values between 0.2 and 84%, FTIR spectroscopy measurements were employed in the downstream region of the discharge. The experimental analyses were accompanied by modelling of the particle number densities. In addition to the electron component, the global plasma-chemical model for dry air involves 50 heavy particle species. The modelling results reveal the importance of different production and loss processes of RONS as well as the influence of the gas temperature and the residence time of plasma in the discharge region on the particle number densities. In the case of humidified air, the model for dry air was extended by 29 HCS. It is found that except for O₃, the number densities of the RONS and HCS increase with increasing RH value.